Microsoft's David Weller has posted an FAQ regarding the XNA development of Zune games in the official XNA Creator Club Online forum:
"Developers will now have the capability to develop once for all three platforms: the Xbox 360, Windows, and Zune. While developers can write one game and target any platform, cross-platform networking between all three platforms is not supported.
Keeping with Zune media experience, XNA Game Studio 3.0 integration includes discoverability and access to user's music allowing the user to customize background soundtracks or create real-time visualizations. In addition, the XNA Community Games Platform team has announced the ability to have multiple Zunes wirelessly engage in an ad-hoc gaming experience.
A preview release of XNA Game Studio 3.0 will be available in the Spring 2008 timeframe, with a final release scheduled for the holiday 2008 season."